Facsimile signal inverter



A E- 7, 1942. F, L. RIE N 2,279,242

FAQSIMILE SIGNAL INVERTER Filed Sept. 2,A1959 INVENTOR F.L. O'BRIEN BYORN Patented Apr. 7,,

UNITED STATE s PATENT OFFICE aziazrz FACSDIILE SIGNAL INVERTER.

Frederic 1.. O'Brien, Rutherford, N. 1., am...

.to The Western Union Telegraph Company,

New York, N. Y., a'corporatlon of New York,

' Application September 2,1939, Serial No. 293,166

, 8 Claims. (Cl. 178-6.6)

modulation in accordance with the quantity of light reflected from thesubject matter onto the photoelectric cell. Thus, an elemental area fromwhich a large quantity of light is reflected is represented by signalshaving a relatively large amplitude and, conversely, a relatively darkelemental area is represented by signals having a relatively smallamplitude. Such signals may be employed to record on a photographic filmor equivalent recording means for the purpose of 0btaining a negativecopy of the scanned subject matter. However, in ,order to obtain apositive copy or an exact reproduction of the scanned subject matter itis necessary to make a positive print from the film or other recordingmeans.

In order to eliminate this additional step the facsimile signalsrepresentative of the scanned subject matter may be inverted. Numeroussig-' nal inverting systems have been proposed heretofore for invertingthe signals as they are generated at the transmitter, but it is notalways convenient to employ such apparatus because of the fact thatskilled operators may not be available at the transmitting point to makethe necessary telegraph signals subsequent to the generation- V thereof.

Another object of the invention resides in the I provision of means foroperating facsimile sigadjustments. Also, it is often desirable toeffect :1

the simultaneous recording of facsimile signals to obtain both anegative and a positive copy of the transmitted subject matter. For theforegoin reasons and also because it may be more feasible to locate thesignal inverting apparatus at the receiving point'where the recordedcopy may be used as a guide in making the necessary adjustments, it isdesirable that-means be provided for inverting the facsimile signals atthe receiving 4 station. It is also advantageous, in employing apparatuswhich is used for such a purpose at a point remote from the transmittingstation, to maintain the apparatus in exact synchronism with thegenerator of the signals. In'this way, any variation in the frequency ofthe modulated carrier wave is compensated-for in the signal invertingapparatus.

Hence it is the primary object of the invention 55 be convenientlymounted on a drum I. The drum to provide novel means for invertingfacsimile naling apparatus in exact synchronism with the si nalgenerator.

Still another object of the invention is to pro-- vide means forgenerating direct current modulated in accordance with the facsimilesignals and for combining the generated direct current with thefacsimile signals in a manner to produce other signals modulatedinversely to the facsimile signals.

A further object of this invention isto' pro-' vide means for derivingfrom the facsimile si nals a direct current modulated in accordance Awith the facsimile signals.

Other and more specific objects of the instant invention will appear inthe following description of .the invention taken in conjunction withthe accompanying drawing. the single figure-of which shows the circuitarrangement of. a facsimile telegraph system embodying an illustrativeform of the novel facsimile signal inverting apparatus.

In its general aspect the invention contemplates the derivation fromamplitude modulated facsimile signals of a modulated direct current.

The facsimile signals are impressed upon the input circuit of athermionic amplifier. Also the I modulated direct current is connectedto the input circuit of the amplifier in a manner to oppose thefacsimile signals. Thus, the modulated direct 7 current constitutes abias modulation for the amplifier and is sufllciently large when thefacsimile signals are at a maximum so that the facsimile signals aregiven a very small amplification.

When the facsimile signals are small in ampliversely in amplitude to thegenerated facsimile signals.

' The invention is disclosed and described in conjunction with afacsimile telegraph system employing an optical scanning device. It willbe understood that the instant invention is not limited to the specificcombination of instrumentalities disclosed herein but may be practicedin combination with substantially any form of'facsimile scanningapparatus. Referring to the drawing. the subject matter to be scannedmay is rotated at a suitable speed by means of a driving motor 2 whichis connected thereto by means of a coupling device 3. Axial movement ofthe drum i is produced by a suitable means 4 so that the entire field ofthe message may be scanned. Light from a source 6 is concentrated bymeans of a lens 1 upon the surface to be scanned and is reflected into aphotoelectric cell I or equivalent device. The spot of light which isprojected upon the surface of the cylinder or drum I is thus caused totraverse the cylinder in a longitudinal direction as the cylinderrotates by reason of the axial movement thereof. The light which isreflected from the surface of the subject matter being scanned and whichis incident upon the photoelectric cell 8 is interrupted by a shutter orlight chopper 9. The shutter may be in the form of a disc as illustratedwhich is provided with a series of equally spaced openings or notches lladjacent its outer edge. In cases where the reflected light is to beinterrupted, a lens I! serves to bring the reflected light beam to afocus substantially in the plane of the disc 9 so that it may passthrough openings ll successively. The disc 8 is mounted upon a rotatableshaft i3 which may be driven in any suitable mannerfrom the motor 2 or,if desired, from a separatesource of mechanical power. The number ofopenings in the disc and the speed of rotation of the shaft may varywithin wide limits depending upon the desired rate of scanning, theconstants of the communication circuit employed between the transmittingand receiving stations and other factors. The output appearing acrossthe terminals of the photoelectric cell 8 is of such a character that anegative copy of the scanned subject matter will be reproduced by theusual recorder employed in facsimile systems of thisnature.

In cases where it is desired to make a positive record from facsimilesignals generated as 'de-' scribed, a signal inverter is employed,anovcl form of which comprises the subject matter of the instantinvention. Subsequent to the generation of the facsimile signalsmodulated in accordance with the tone values of the subject matterscanned the signals may be amplified by means of a suitable amplifier l4and transmitted over a pair of line conductors I6. At the receivingstation the line conductors are terminated in windings l1 and I8 oftransformers l8 and 2| rebe provided for these purposes withoutdeparting from the spirit of the invention.

The facsimile signals which are impressed upon the winding ll 'oftransformer I! are inductively reproduced in the winding ll of thistransformer. The terminals of the winding 3' are connected to thecontrol grid elements 31 and 3. of a pair of amplifying tubes 39 and 4|respectively. The midpoint of the transformer winding 36 is confacsimilesignals is connected across thefresis tance element 42 and in a mannerto produce a negative bias upon the input circuits of the tubes 39 and 4I, which is in opposition to the facsimile signals impressed upon theinput circuits. Thus.

it may be seen that when the amplitude of the' facsimile signals islarge, a relatively large nega-'-' tive bias is applied to theamplifying tubes 38 and 4| so that the facsimile signals are given aminimum of amplification. However, when the am-' plitude of thegenerated facsimile signals is small, the bias which is applied to thetubes is also small since it is derived from the facsimile signals.

spectively The modulated facsimile signals are reproduced; by inductionin the winding 22 of transformer 2| which-is connected to the inputcircuit of a thermionic device 23. The output circuit of the tube 23includes an anode or plate 24, the winding 26 of transformer 21 and asource of plate potential 28. v The modulated alternating currentsignals amplified by the tube 23 are reproduced inductively in thewinding 28 of transformer 21. The terminals of this winding areconnected respectively to plates 3! and 32 of the tube 23. The winding28 is provided with a tap intermediate its terminals and which isconnected to one terminal of a potentiometer 33. the other terminal ofwhich is connected to the cathode 34 of the tube 23.

Thus, by this arrangement the alternating current signals are rectifiedand appear across the potentiometer 33 as a direct current potentialmodulated in accordance with modulations of the facsimile signals. Ithas been found convenient to include the amplifier and the rectifier inone envelope. However, it will be obvious to those skilled in the artthat separate tubes may Gonsequently, the small amplitude facsimilesignals are given a relatively large amplification. In this manner thefacsimile signals are ei'fec-' tively inverted. The inverted signals arereproduced in the winding 41 of transformer 44 andmay be amplified ifdesired by means of an am plifier 48 and applied to the recordingapparatus. The recording apparatus as disclosed herein is substantiallysimilar to the transmitting apparatus previously described with theexception that, instead of the optical scanning instrumentalities, theapparatus is provided with a stylus 49 by means of which recording maybe effected electrically in a manner well known in the art. Thus, it isseen that by employing the signal inverting apparatus described, therecording apparatus functions in such a manner that marks are made onthe recording medium having tone values varying between white and blackin accordance with the variation in the current amplitude of the signalsimpressed upon the recording stylus 49.

The nature of the invention may be ascertained from the foregoingdescritpion of an illustrative embodiment, it being understood thatchanges in the invention herein disclosed may be made within the scopeof what is claimed without departing from the spirit of the invention.

What is claimed is: l 1. In a facsimile telegraph system, means forgenerating signaling current modulated in amplitude in accordance withthe amount of light reflectedfron elemental areas of the scanned subjectmatter, a vacuum tube arrangement to amplify a small portion of saidsignaling current thereof inverse to the amplitude ratio of componentsof the generated signaling current.

2. In a facsimile telegraph system, means for generating alternatingcurrent modulated in amplitude in accordance with the amount of lightreflected from elemental areas of the scanned subject matter, twoamplifiers, means for impressing said alternating current upon saidamplifiers simultaneously, means including a' first one of saidamplifiers for amplifying a small portion of said alternating currentenergy, a rectifier for said amplified energy and means includingconnections between said rectifier and the second one of said amplifiersto vary the degree of amplification of said second amplifier in inverseproportion to the generated alternating current to produce alternatingcurrent modulated in amplitude inversely to said generated alternatingcurrent.

3. In a facsimile telegraph system, means for generating alternatingcurrent facsimile signals modulated in amplitude in accordance with tonevalues of subject matter, a rectifier for trans-- lating said facsimilesignals to direct current modulated in accordance with said signals, apair of vacuum tubes, eachhaving input and output circuits, means forimpressing said modulated.

means connected differentially to said output cir-' cuits to translatethe combined output of said tubes into alternating current recordingsignals modulated in amplitude inversely to said generated facsimilesignals.

4. Ina facsimile telegraph system utilizingamplitude modulatedalternating current signals, signal-inverting apparatus comprising, a

' thermionic amplifier, a rectifier, a utilization circuit, means forimpressing said modulated alternating current signals simultaneouslyupon said amplifier and said rectifier, means including said rectifierfor negatively biasing said amplifier constantly in proportion to theinstantaneous amplitude of said signals whereby said signals areamplified in inverse proportion to the amplitude of said facsimilesignals, and means for impressing said amplified signals upon saidutilization circuit.

5. A facsimile telegraph system comprising, means for generatingalternating current facsimile signal energy modulated in amplitude inaccordance with tone values of subject matter, an amplifier having inputand output circuits, means for rectifying one portion of said facsimilesignal energy to obtain direct current energy proportional in amplitudeto said facsimile signal energy, means for combining in simultaneousopposition in the input circuit of said amplifier another portion ofsaid facsimile signal energy and the corresponding direct current energyderived from said one portion of said facsimile signal energy to producein the output circuit of said amplifier signals having amplitudesinversely related to the amplitude of said facsimile signal energy, andmeans for recording the inverted signals. 4

6. A; facsimile telegraph system comprising, means for generatingalternating current facsimile signals modulated in amplitude inaccordance with tone values of subject matter, means for amplifying saidsignals, means controlled by said signals for producing a direct currentvarying in magnitude in proportion to the instantaneous amplitude ofsaid signals, means simile signal energy, and circuits interconnectingsaid rectifier-and said grid to utilize said'demodulated facsimilesignal energy as a variable negative bias for said grid, said biasconstantly varying in direct proportion to the amplitude of saidfacsimile signal, energy to vary constantly the amplification factor ofsaid amplifier in inverse proportion to the amplitude of said facsimilesignal energy whereby the amplified signal energy is modulated inamplitude inversely to said facsimile signal energy.

8. In a facsimile telegraph system, means for.

generating amplitude modulated alternating current energy constitutingfacsimile signals representative of scanned subject matter, anamplifier, means including said amplifier for amplifying one portion ofsaid signal energy, means for rectifying another portion of said signalenergy, and means for utilizing said rectified signal energy as a biasfor said amplifier to-vary the degree of amplification thereof inverselyto the amplitude of the facsimile signals whereby the amplified signalenergy is modulated in amplitude inversely to said facsimile signals;

FREDERIC L. O'BRIEN.

